Method for treating process condensate

• US 5,643,420 A
• Filed: 10/06/1995
• Issued: 07/01/1997
• Est. Priority Date: 09/03/1993
• Status: Expired due to Fees

• Current Assignee: Farmland Industries Incorporated
• Original Assignee: Farmland Industries Incorporated
• Inventors: Holiday, Allan D.
• Primary Examiner(s): Warden, Robert J.
• Assistant Examiner(s): TRAN, HIEN THI
• Application Number:
  US08/539,830
• Time in Patent Office: 634 Days
• Field of Search: 203/10, 203/11, 203/12, 203/14, 203/75-76, 203/92-94, 203/98, 203/DIG. 6, 423/352, 423/359, 568/913, 518/705, 518/704, 422/187
• US Class Current: 203/11
• CPC Class Codes: B01D 3/38 Steam distillation

Abstract

An apparatus and method for treating chemical production plant process condensate such that a contaminant-rich stream and a relatively pure aqueous stream is separately recoverable from the condensate, wherein the contaminants are substantially removed from the condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/rectification tower. The tower overhead is then condensed, and any non-condensed gases are subjected to water scrubbing to further recover contaminates from the non-condensed gas. A portion of the condensed overhead and scrubbing water containing contaminates is returned to the top of the rectification section of the tower as reflux and the balance being withdrawn as a concentrated stream for reuse in the plant. The apparatus may be used in conjunction with existing low pressure equipment, avoiding costly major modifications, and is particularly adapted to use in conjunction with ammonia and methanol plants.

Claims

1. A method for treating a chemical production plant process effluent stream of dilute contaminants, said method comprising the following steps:

stripping at least a portion of contaminants from a process effluent obtained from a chemical production plant, wherein said stripping is conducted in a stripping section to obtain a contaminant-rich vapor stream and an aqueous bottom stream of reduced contaminant content;

rectifying said contaminant-rich vapor stream in a rectification section to obtain a concentrated overhead stream;

condensing said concentrated overhead stream to obtain contaminant-rich overhead condensate and non-condensed gases comprising trace amounts of the contaminates;

scrubbing said non-condensed gases so as to recover a portion of said trace amounts of the contaminates into said contaminant-rich overhead condensate;

recycling said overhead condensate to said rectifying step to form a closed loop so as to build up the concentration of contaminants in said overhead condensate;

separating and withdrawing from said closed loop a fraction of said overhead condensate; and

reusing said fraction of the overhead condensate in the chemical production plant.

2. A method according to claim 1, wherein said method additionally comprises collecting said aqueous bottom stream of reduced contaminant content and reusing said bottom stream in said chemical production plant.

3. A method according to claim 2, wherein said aqueous bottom stream is used as scrubbing water for said scrubbing step.

4. A method according to claim 1, wherein said stripping section and said rectification section are housed one above another respectively in a common upright tower permitting vapor from said stripping section to pass upwardly within the common tower to the rectification section above and condensate from each section to pass downwardly within the common tower.

5. A method according to claim 1, wherein said stripping section and said rectification section are provided in separate columns in series.

6. A method according to claim 5, wherein said rectification step is conducted in the rectification section to obtain the concentrated overhead stream and a second aqueous bottom stream of reduced contaminant content, said second aqueous stream being returned to said stripping step.

7. A method according to claim 1, wherein said reusing step comprises injecting said fraction of overhead condensate withdrawn from said closed loop back into said chemical production plant.

8. A method according to claim 7, wherein said reusing step comprises pumping said fraction of overhead condensate under pressure for entry into said plant.

9. A method according to claim 1, wherein said separating and withdrawing step comprises separating and withdrawing from said closed loop a fraction of said overhead condensate in an amount ranging from 3 to 50% by volume of the overhead condensate in said loop.

10. A method according to claim 9, wherein said separating and withdrawing step comprises separating and withdrawing from said closed loop a fraction of said overhead condensate in an amount ranging from 5 to 20% by volume of the overhead condensate in said loop.

11. A method according to claim 1 wherein said stripping section is operable at pressures ranging from 0 psia to 300 psig.

12. A method according to claim 1, wherein said chemical production plant is selected from the group consisting of an ammonia production plant and a methanol production plant.

13. A method according to claim 12, wherein said fraction of the overhead condensate is delivered to the chemical production plant by delivering said fraction to a mixed feed coil of a primary reformer of said plant.

14. A method according to claim 12, wherein said fraction of the overhead condensate is delivered to the chemical production plant by delivering said fraction to an air preheat coil of a secondary reformer of said ammonia plant.

15. A process for stripping ammonia plant process effluent comprised of water and contaminants, said method comprising the steps of:

feeding ammonia plant process effluent from an ammonia plant to the upper stages of a relatively low pressure steam stripping tower equipped with a bottom collection basin and operating at pressures ranging from 0 psia to 300 psig;

allowing said effluent to flow downwardly through a stripping section of said stripping tower against an upward flow of steam to obtain a contaminant-rich vapor stream, and an aqueous bottom stream of reduced contaminant content;

rectifying said contaminant-rich vapor stream in a rectification zone such that contaminants from the effluent pass upwardly through the rectification zone to form an overhead vapor and condensate formed within said rectification zone is passed downwardly and returned to said stripping section;

condensing said overhead vapor to form condensed overhead and non-condensed gases comprising trace amounts of the contaminates;

scrubbing said non-condensed gases in a manner to recover a portion of said trace amounts of the contaminates into the condensed overhead;

continuously recycling said condensed overhead as reflux to said rectification zone to form a closed loop which acts to build up a concentration of the contaminants in said condensed overhead;

continuously separating and withdrawing from said closed loop a fraction of the concentrated condensed overhead;

and

reusing said fraction of said condensed overhead in said ammonia plant.